Multi-Rate Crest Factor Reduction

ABSTRACT

A computer-implemented method for reducing crest factor by an electronic device includes: receiving a plurality of first samples of a first input signal. The plurality of first samples are generated at a first sampling rate. A first peak detection is performed based on the plurality of first samples to generate a plurality of first peak detection output samples. A plurality of first windowing input samples are generated at a second sampling rate by downsampling the plurality of first peak detection output samples. A plurality of first windowing output samples are generated based on the plurality of first windowing input samples. A plurality of first peak reduction samples are generated at the first sampling rate by upsampling the plurality of first windowing output samples. A first output signal is generated based on the plurality of first samples and the plurality of first peak reduction samples.

PRIORITY CLAIM

This application is a national phase filing under section 371 of PCTApplication No. PCT/US2020/018423, filed on Feb. 14, 2020 and entitled“Multi-Rate Crest Factor Reduction,” which is hereby incorporated byreference herein as if reproduced in its entirety.

TECHNICAL FIELD

The present disclosure relates to wireless communication, and morespecifically to improve efficiency and/or linearity of transmitters.

BACKGROUND

In a communication system, a crest factor of a signal may represent aratio of peak values to the effective value of the signal. In somecases, a crest factor may be calculated by dividing the peak amplitudeof a signal by the root mean square of the signal. Therefore, the crestfactor may indicate a peak-to-average power ratio of the signal. Asignal with a high crest factor may distort the linearity of a poweramplifier in a transmitter. Therefore, in some cases, a transmitter mayreduce the crest factor of a signal before transmitting the signal.

SUMMARY

The present disclosure is directed to methods and systems for reducingcrest factors.

In a first implementation, a method for reducing crest factors includes:receiving plurality of first samples of a first input signal, whereinthe plurality of first samples are generated at a first sampling rate;performing a first peak detection based on the plurality of firstsamples to generate a plurality of first peak detection output samples;downsampling the plurality of first peak detection output samples togenerate a plurality of first windowing input samples at a secondsampling rate; generating a plurality of first windowing output samplesbased on the plurality of first windowing input samples; upsampling theplurality of first windowing output samples to generate a plurality offirst peak reduction samples at the first sampling rate; and generatinga first output signal based on the plurality of first samples and theplurality of first peak reduction samples.

In a second implementation, an electronic device includes: anon-transitory memory storage comprising instructions, and one or morehardware processors in communication with the memory storage, whereinthe one or more hardware processors execute the instructions to: receivea plurality of first samples of a first input signal, wherein theplurality of first samples are generated at a first sampling rate;perform a first peak detection based on the plurality of first samplesto generate a plurality of first peak detection output samples;downsample the plurality of first peak detection output samples togenerate a plurality of first windowing input samples at a secondsampling rate; generate a plurality of first windowing output samplesbased on the plurality of first windowing input samples; upsample theplurality of first windowing output samples to generate a plurality offirst peak reduction samples at the first sampling rate; and generate afirst output signal based on the plurality of first samples and theplurality of first peak reduction samples.

In a third implementation, a non-transitory computer-readable mediumstoring computer instructions for reducing crest factor, that whenexecuted by one or more hardware processors, cause the one or morehardware processors to perform operations including: receiving aplurality of first samples of a first input signal, wherein theplurality of first samples are generated at a first sampling rate;performing a first peak detection based on the plurality of firstsamples to generate a plurality of first peak detection output samples;downsampling the plurality of first peak detection output samples togenerate a plurality of first windowing input samples at a secondsampling rate; generating a plurality of first windowing output samplesbased on the plurality of first windowing input samples; upsampling theplurality of first windowing output samples to generate a plurality offirst peak reduction samples at the first sampling rate; and generatinga first output signal based on the plurality of first samples and theplurality of first peak reduction samples.

The previously described implementation is implementable using acomputer-implemented method; a non-transitory, computer-readable mediumstoring computer-readable instructions to perform thecomputer-implemented method; and a computer-implemented systemcomprising a computer memory interoperably coupled with a hardwareprocessor configured to perform the computer-implemented method and theinstructions stored on the non-transitory, computer-readable medium.

The details of one or more implementations of the subject matter of thisspecification are set forth in the accompanying drawings and thedescription. Other features, aspects, and advantages of the subjectmatter will become apparent from the description, the drawings, and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example wireless communication system that reduces crestfactors according to an implementation.

FIG. 2 is a schematic diagram illustrating an example carrieraggregation transmitter according to an implementation.

FIG. 3 is a graph showing a carrier aggregation signal characterizationof an example carrier aggregation transmitter according to animplementation.

FIG. 4 is a graph showing an example crest factor reduction (CFR) anddigital predistortion (DPD) co-operation algorithm according to animplementation.

FIG. 5 is a schematic diagram illustrating an example CFR componentaccording to an implementation.

FIG. 6 shows performance of an example CFR component according to animplementation.

FIG. 7 is a schematic diagram illustrating an example windowing signalgenerator according to an implementation.

FIG. 8 shows CFR performance of an example CFR component with respect towindow length of the example CFR component according to animplementation.

FIG. 9 shows CFR performance of an example CFR component with respect tosampling rate of the example CFR component according to animplementation.

FIG. 10 shows CFR waveforms at different sampling rates according to animplementation.

FIG. 11 is a graph illustrating an example spectrum analysis for CFR atdifferent sampling rates according to an implementation.

FIG. 12 shows an example CFR with upsampling according to animplementation.

FIG. 13 shows an example upsampling CFR with a first upsampling ratioaccording to an implementation.

FIG. 14 shows an example upsampling CFR with a second upsampling ratioaccording to an implementation.

FIG. 15 shows an example upsampling CFR cascaded with digital upconverter according to an implementation.

FIG. 16 is a schematic diagram illustrating an example two-carriermulti-rate CFR component according to an implementation.

FIG. 17 is a schematic diagram illustrating an example two-carriercombined signal peak detection component according to an implementation.

FIG. 18 shows the waveforms in an example peak detection processaccording to an implementation.

FIG. 19 is a flowchart illustrating an example method for peak detectionaccording to an implementation.

FIG. 20 is a schematic diagram illustrating an example windowing signalgenerator according to an implementation.

FIG. 21 is a schematic diagram illustrating an example multi-carriermulti-rate CFR component according to an implementation.

FIG. 22 is a schematic diagram illustrating an example multi-carriercombined signal peak detection component according to an implementation.

FIG. 23 shows a comparison of performance of single-rate and multi-rateCFR according to an implementation.

FIG. 24 shows a comparison of performance of single-rate and multi-rateCFR according to an implementation.

FIG. 25 is a flow chart illustrating an example method for reducingcrest factors according to an implementation.

FIG. 26 is a schematic diagram illustrating an example structure of anelectronic device according to an implementation.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following detailed description describes multi-rate crest factorreduction for improving efficiency and/or linearity of transmitters andis presented to enable any person skilled in the art to make and use thedisclosed subject matter in the context of one or more particularimplementations.

Various modifications, alterations, and permutations of the disclosedimplementations can be made and will be readily apparent to those ofordinary skill in the art, and the general principles defined may beapplied to other implementations and applications, without departingfrom scope of the disclosure. In some instances, details unnecessary toobtain an understanding of the described subject matter may be omittedso as to not obscure one or more described implementations withunnecessary detail inasmuch as such details are within the skill of oneof ordinary skill in the art. The present disclosure is not intended tobe limited to the described or illustrated implementations, but to beaccorded the widest scope consistent with the described principles andfeatures.

In some cases, a crest factor reduction (CFR) algorithm may be used toreduce the dynamic range of a signal that has a high Peak to AveragePower Ratio (PAPR). Reducing the crest factor of a signal can improvethe linearity of the radio frequency (RF) power amplifier in atransmitter. In some cases, multi-stage CFR algorithms can be used toreduce the PAPR of a transmission signal. However, a multi-stage CFRalgorithm may use variable parameters for signals with differentbandwidth.

FIG. 1 is an example wireless communication system wo that reduces crestfactors according to an implementation. For example, an input signal maybe received. The input signal may include a clipping signal that reducesa peak amplitude of a source signal based on a predetermined clippinglevel. The input signal may be transposed to a plurality of transposedsignals using a plurality of multipliers. In some cases, each of theplurality of multipliers may have a windowing function coefficient, andeach of the plurality of transposed signals may be generated bymultiplying the input signal with the respective windowing functioncoefficient of each of the plurality of the multipliers. In some cases,at least one of the plurality of multipliers may be implemented usingcanonic signed digit (CSD) arithmetic. In some cases, at least one ofthe plurality of multipliers may be implemented using a multiplicationfunction unit. A feedback signal may be generated based on the pluralityof transposed signals using a first plurality of delay taps. A windowingsignal may be generated based on the feedback signal. The windowingsignal may reduce a crest factor of the source signal. In some cases, aforward path signal may be generated using the plurality of transposedsignals, the first plurality of delay taps, and a second plurality ofdelay taps. In some cases, the windowing signal may be generated basedon the forward path signal. In some cases, an output signal may begenerated based on the windowing signal and the source signal.

Reducing crest factors according to methods and systems described hereinmay provide one or more advantages. For example, transposing the signalbefore passing the signal through the delay taps may reduce the delaycreated in the critical path of the finite impulse response (FIR)filter. In addition, using a folding structure may reduce the number ofmultipliers in the FIR filter and therefore reduces implementationcomplexity of the filter. Furthermore, using CSD arithmetic may replacemultiplication function units with addition and subtraction functionunits, and therefore reduces the delay and the implementationcomplexities of the filter. Reducing the delay may improve the speedperformance of the FIR filter and enable the filter to be used toprocess a broadband signal that has a stringent delay requirement.

At a high level, the example wireless communication system 100 includesa user device 102 and a wireless communication network no, whichincludes a base station 104 that is configured to communicate with theuser device 102. In the illustrated example, the user device 102 mayperform a CFR operation on an uplink signal before transmitting theuplink signal to the base station 104. Similarly, the base station 104may perform a CFR operation on a downlink signal before transmitting thedownlink signal to the user device 102.

For example, the user device 102 may include a windowing signalgenerator. A windowing signal generator may include one or more hardwarecircuit elements, software, or a combination thereof that can beconfigured to create a signal waveform with window shaping. Thewindowing signal generator may receive an input signal. The input signalmay include a clipping signal that reduces a peak amplitude of a sourcesignal based on a predetermined clipping level. In some cases, thesource signal may be a signal whose crest factor will be reduced beforebeing transmitted. The input signal may be transposed to a plurality oftransposed signals using a plurality of multipliers. A feedback signalmay be generated based on the plurality of transposed signals using afirst plurality of delay taps. A windowing signal may be generated basedon the feedback signal. In some cases, the user device 102 may use thewindowing signal and the input signal to generate an output signal. Theoutput signal has a reduced crest factor. The user device 102 maytransmit the output signal using a transmit antenna.

Similarly, the base station 104 may also include a windowing signalgenerator that generates a windowing signal as discussed above. The basestation 104 may use the windowing signal and the input signal togenerate an output signal that has a reduced crest factor. The basestation 104 may transmit the output signal using a transmit antenna.

Turning to a general description of the elements, a user device may bereferred to as a mobile electronic device, user device, mobile station,subscriber station, portable electronic device, mobile communicationsdevice, wireless modem, or wireless terminal. Examples of a UE (e.g.,the UE 102) may include a cellular phone, personal data assistant (PDA),smart phone, laptop, tablet personal computer (PC), pager, portablecomputer, portable gaming device, wearable electronic device, or othermobile communications device having components for communicating voiceor data via a wireless communication network. The wireless communicationnetwork may include a wireless link over at least one of a licensedspectrum and an unlicensed spectrum.

Other examples of a user device include mobile and fixed electronicdevices. A UE may include a Mobile Equipment (ME) device and a removablememory module, such as a Universal Integrated Circuit Card (UICC) thatincludes a Subscriber Identity Module (SIM) application, a UniversalSubscriber Identity Module (USIM) application, or a Removable UserIdentity Module (R-UIM) application. The term “user device” can alsorefer to any hardware or software component that can terminate acommunication session for a user.

The wireless communication network no may include one or a plurality ofradio access networks (RANs), core networks (CNs), and externalnetworks. The RANs may comprise one or more radio access technologies.In some implementations, the radio access technologies may be GlobalSystem for Mobile communication (GSM), Interim Standard 95 (IS-95),Universal Mobile Telecommunications System (UMTS), CDMA2000 (CodeDivision Multiple Access), Evolved Universal Mobile TelecommunicationsSystem (UMTS), Long Term Evaluation (LTE), or LTE Advanced. In someinstances, the core networks may be evolved packet cores (EPCs).

A RAN is part of a wireless telecommunication system which implements aradio access technology, such as UMTS, CDMA2000, 3GPP LTE, and 3GPPLTE-A. In many applications, a RAN includes at least one base station104. A base station 104 may be a radio base station that may control allor at least some radio-related functions in a fixed part of the system.The base station 104 may provide radio interface within their coveragearea or a cell for the user device 102 to communicate. The base station104 may be distributed throughout the cellular network to provide a widearea of coverage. The base station 104 directly communicates to one or aplurality of user devices, other base stations, and one or more corenetwork nodes.

While described in terms of FIG. 1 , the present disclosure is notlimited to such an environment. The base station 104 may operate on anyof the different wireless communication technologies. Example wirelesstechnologies include Global System for Mobile Communication (GSM),Universal Mobile Telecommunications System (UMTS), 3GPP Long TermEvolution (LTE), LTE-Advanced (LTE-A), wireless broadband communicationtechnologies, and others. Example wireless broadband communicationsystems include IEEE 802.11 wireless local area network, IEEE 802.16WiMAX network, and others.

While elements of FIGS. 1-26 are shown as including various componentparts, portions, or modules that implement the various features andfunctionality, nevertheless these elements may instead include a numberof submodules, third-party services, components, libraries, and such, asappropriate. Furthermore, the features and functionality of variouscomponents can be combined into fewer components as appropriate.

FIG. 2 is a schematic diagram illustrating an example carrieraggregation transmitter 200 according to an implementation. In somecases, the carrier aggregation transmitter 200 can be used to apply acrest factor reduction (CFR) algorithm to reduce peak-to-average powerratio (PAPR) of a modulation signal and work with digital pre-distortion(DPD) to improve linearity/efficiency of radio frequency power amplifier(RFPA) with better adjacent channel leakage ratio (ACLR) and lower costand power consumption. As illustrated, the carrier aggregationtransmitter 200 includes interpolators 202-1˜N, multipliers 204-1˜N, asummation function unit 206, a CFR component 208, a DPD component 210, adigital-to-analog converter (DAC) 212, a multiplier 214, a RFPA 216, andan antenna 218. In some cases, the CFR component 208 can be used toreduce PAPR of the signal so that the DPD component 210 can linearizeRFPA 216 under a dynamic range.

In some cases, the carrier aggregation in the carrier aggregationtransmitter 200 can improve the throughput of the communication.However, in some cases, the carrier aggregation may lead to a high PAPRproblem. For example, the PAPR may increase with the number of carriersand thus degrade RFPA efficiency and linearity. FIG. 3 is a graphshowing a carrier aggregation signal characterization of an examplecarrier aggregation transmitter (e.g., carrier aggregation transmitter200). Specifically, FIG. 3 illustrates a complementary cumulativedistribution function (CCDF) curve of signals for different numbers ofcarriers from one to five, where the horizontal axis is scaled to dBabove the average signal power, which means that the peak-to-averageratios as opposed to absolute power level is being measured. Thevertical axis is the percentage of time the signal spends at or abovethe power level specified by the horizontal axis. As shown, the PAPR ofthe signal increases with the number of the carriers. To meet linearityrequirements, RFPA may consume more power while operating with highPAPR. This may lead to lower efficiency problem and reduce batterylifetime. Furthermore, the maximal linear output power may be reducedwith high PAPR and the coverage range may shrink, which can increase thedropped-call rate (DCR) of communication.

In some cases, CFR can be used to reduce PAPR of a modulation signal andwork with DPD to improve RFPA performance. FIG. 4 is a graph showing anexample CFR and DPD co-operation algorithm. As shown, a power amplifieramplitude to amplitude modulation (PA AMAM) characterization, an indexDPD function, input signals (with and without CFR), and output signals(with and without CFR) are illustrated on the left side. In an exampleDPD operation, the pre-distortion signal of the input at A can index Bfrom the DPD function. DPD mapping can be used to invoke the RFPA outputpower at C, which is the maximal RFPA output power. In some cases,compression/clipping may occur when input amplitude is greater than Asince the associated pre-distortion power is greater than the maximumoutput power. As shown by the clipping waveform represented by frequencyresponse cot, (y-axis is the magnitude of frequency) on the right sideof the figure, the DPD will not compensate such distortion (e.g., thecompressed/clipped waveform). The ACLR performance, therefore, can belimited by the compression/clipping. The RFPA efficiency and linearitymay also be degraded. To reduce the low performance and low efficiencyproblems, peaks of the input amplitude can be required to be lower thanA. In some cases, CFR can be used to reduce the magnitude of the peaksto be lower than A to enhance DPD performance and reduce the PAPR. Withlow PAPR of the modulation signal, RFPA can operate at higher outputpower region and enhance the transmitter coverage.

FIG. 5 is a schematic diagram illustrating an example CFR component 500according to an implementation. In some cases, the CFR component 500 canbe used in a transmitter, e.g., in the user device 102 or in the basestation 104 or in the transmitter 200, to reduce the peak amplitude of asource signal x(n). As illustrated, the CFR component 500 includes anamplitude calculator 502, a clipping signal generator 504, and awindowing signal generator 506. The amplitude calculator 502, theclipping signal generator 504, and the windowing signal generator 506can be used to generate a windowing signal b(n) based on the sourcesignal x(n) and a clipping level. The CFR component 500 also includespipeline delay registers 508 a-b and multipliers 510 a-b that are usedto mix the source signal x(n) with the windowing signal b(n) to generatean output signal y(n) that has a reduced crest factor.

As illustrated, the I and Q components of the source signal x(n) passthrough the amplitude calculator 502 to generate the amplitude level|x(n)| of the source signal x(n). In some cases, the amplitudecalculator 502 may include one or more hardware circuit elements,software, or a combination thereof that can be configured to generate anamplitude level of a signal.

In some cases, the clipping signal generator 504 may include one or morehardware circuit elements, software, or a combination thereof that canbe configured to generate a clipping signal. As illustrated, theclipping signal generator 504 receives the amplitude level |x(n)| and aclipping level to generate a clipping signal c(n). In some cases, theclipping level represents a predetermined peak value for the outputsignal y(n). In some cases, the clipping signal c(n) represents ascaling function, which may scale down the components in the sourcesignal x(n) that are above the clipping level.

The following equation represents an example clipping signal c(n).

${c(n)} = \left\{ {\begin{matrix}{1,} & {\ {{❘{x(n)}❘} \leq \ {{Clipping}\ {Level}}}} \\{\frac{{Clipping}{Level}}{❘{x(n)}❘},} & {\ {{❘{x(n)}❘} > \ {{Clipping}\ {Level}}}}\end{matrix}.} \right.$

In some cases, for example, in a hard-clipping CFR algorithm, the sourcesignal x(n) is multiplied with the clipping signal c(n) to generate anoutput signal. However, the output signal produced in the hard clippingCFR algorithm may include an increased out-of-band signal level. Thismay be referred to as adjacent channel power re-growth problems. Becausethe out-of-band signal level is increased, the noise floor of the outputsignal is degraded. In some cases, an output signal with increasedout-of-band signal level may fail an out-of-band emission maskrequirement specified by a radio access technology standard, andtherefore cannot be transmitted in the corresponding wirelesscommunication system.

In some cases, a windowing signal may be used to reduce the adjacentchannel power re-growth effects. In some cases, as illustrated in FIG. 5, the windowing signal generator 506 may receive the clipping signalc(n) and generate the windowing signal b(n) based on the clipping signalc(n). In some cases, the windowing signal generator may be implementedusing a finite impulse response (FIR) filter. The FIR filter may includeN windowing function units. Each of the windowing function unit may havea windowing function coefficient. The windowing function coefficient maybe denoted as W₀, W₁, W₂, . . . , W_(N-1), where N represents the orderof the FIR filter. In some cases, the order of the FIR filter denotesthe number of windowing function units used in the FIR filter. Thefollowing equation represents an example windowing signal b(n):

${b(n)} = {1 - {\sum\limits_{k = {- \infty}}^{\infty}{\left\lbrack {1 - {c(n)}} \right\rbrack{w\left( {n - k} \right)}}}}$

In the above equation, b(n) is the output of the clipping signal afterwindowing process, c(n) is the clipping function determined by athreshold level, and w(n-k) is the window function. In some cases, thewindow function may be generated by the Hamming or Hanning function.

As illustrated, the source signal x(n) passes through pipeline delayregisters 508 a-b, and feed into the multipliers 510 a-b, respectively.The multipliers 510 a-b multiply the delayed source signals with awindowing signal b(n) to generate output signal y(n). The output signalhas a reduced crest factor compared to the source signal x(n). Thefollowing equation represents an example output signal y(n):

y(n)=x(n)b(n).

In some cases, the windowing-based CFR algorithm can provide peakreduction with ACLR improvement. FIG. 6 shows performance of an exampleCFR component. Graph (a) of FIG. 6 shows the CCDF curve of an LTE signalwith and without CFR. As shown, the PAPR has been reduced by 2 dB afterpeak reduction. Graph (b) of FIG. 6 shows the CFR waveform. Graph (c) ofFIG. 6 shows that the ACLR after peak reduction has been improved.

FIG. 7 is a schematic diagram illustrating an example windowing signalgenerator 700 (e.g., windowing signal generator 506 of FIG. 5 )according to an implementation. As shown, the windowing signal generator700 receives an input signal c(n) and generates a convolution windowoutput. In some cases, the windowing signal generator 700 includes acomparator 702 that is configured to compare input signals. Inoperation, the input signal c(n) is multiplied by −1, and added to 1 togenerate a signal 1−c(n). A feedback signal m is multiplied by −1 andadded to the signal 1−c(n) to generate an input signal to comparator702. The comparator 702 outputs a signal that is either the input signalor 0.

In the illustrated example, N represents the order of the windowingsignal generator 700. As illustrated, the windowing signal generator 700includes N/2 windowing function units. In some cases, each of thewindowing function units may be implemented as a multiplier thatmultiplies a signal with a windowing function coefficient. In operation,each windowing function unit receives a signal outputted from thecomparator 702 and transposes the signal into a transposed signal. Insome cases, the windowing function unit may transpose the signal bymultiplying the signal with its windowing coefficient. As illustrated,the windowing signal generator 700 also includes N delay taps (D). Thetransposed signals pass through half of the N delay taps to generate thefeedback signal m. Using a transposed structure reduces the delaycreated in the feedback path because the critical path remains the samewhile the number of delay taps increases. This approach increases thespeed performance of the windowing signal generator 700 and enables thewindowing signal generator 700 to process signals with a high samplingrate.

In some cases, the CFR performance changes with window length of thewindowing signal generator (e.g., windowing signal generator 700) at afixed sampling rate. In some cases, the window length may be determinedbased on the number of delay taps in the windowing signal generator.FIG. 8 shows CFR performance of an example CFR component with respect towindow length of the example CFR component. Graph (a) of FIG. 8 showsthat a PAPR of 5.9 dB is obtained and the PAPR is reduced byapproximately 2 dB after peak reduction with a window length of 40 taps.Graph (b) of FIG. 8 shows that ACLR is improved (e.g., reduced) whenwindow length is increased, and that error vector magnitude (EVM) isdegraded (e.g., increased) when window length is increased. Graph (c) ofFIG. 8 shows the ACLR performance for CFR with different window lengths(e.g., 10/20/30/40/50 delay taps) at a fixed sampling rate (e.g., 15.36MHz). As shown, the ACLR is improved as the number of delay tapsincreases.

In some cases, the CFR performance changes with sampling rate at a fixedwindow length. FIG. 9 shows CFR performance of an example CFR componentwith respect to sampling rate of the example CFR. As shown, ACLRdegraded when the CFR operates at higher sampling rate. To obtainEVM<−32 dB, CFR with 40 taps is selected for the sampling rate vs.performance study. Graph (a) of FIG. 9 shows that a PAPR of 5.9 dB isobtained and the PAPR is reduced by approximately 2 dB after peakreduction with a window length of 40 taps. Graph (b) of FIG. 9 showsthat ACLR is degraded (e.g., increased) when sampling rate is increased,and that EVM is improved (e.g., decreased) when sampling rate isincreased. Graph (c) of FIG. 9 shows the ACLR performance for CFR withdifferent sampling rates (e.g., 15.36/30.72/61.44/122.88 MHz) at a fixedwindow length (e.g., 40 delay taps). As shown, the lowest sampling rate15.36 MHz provides the best ACLR performance (e.g., lowest ACLR) amongthe four sampling rates.

FIG. 10 shows CFR waveforms at different sampling rates with fixednumber of delay taps (e.g., 40 delay taps). As shown, graph (a) of FIG.10 shows a waveform for 40-tap CFR at 15.36 MHz. As shown, twoupsamplings, each with a factor of 2, are performed after the 40-tapCFR. Graph (b) of FIG. 10 shows a waveform for 40-tap CFR at 30.72 MHz.As shown, a first upsampling is performed by a factor of 2 before the40-tap CFR, and a second upsampling is performed by a factor of 2 afterthe 40-tap CFR. Graph (c) of FIG. 10 shows a waveform for 40-taps CFR at61.44 MHz. As shown, two upsamplings, each with a factor of 2, areperformed before the 40-tap CFR. The window waveform duration decreasesas sampling rate at which the CFR performs increases from (a) to (c).

In some cases, the window waveform duration determines the ACLR. In anexample where CFR with fixed 40 taps is used for peak reduction, thewindow duration can be determined as (1/sample rate)*40 taps. In thisexample, the window duration decreases when the sample rate increases.In some cases, the ACLR performance improves when the window durationincreases. The ACLR performance, therefore, decreases as sampling rateincreases. FIG. 11 is a graph illustrating an example spectrum analysisfor CFR at different sampling rates. As shown, the ACLR performancedegrades with increased sampling rate. In some cases, when CFR operatesat high sampling rate, high order window FIR may be needed to improvethe ACLR performance. However, this may require huge silicon resource toachieve targeting performance.

In some cases, the windowing function of CFR can operate at a lowsampling rate. The output signal of the CFR can then be upsampled to ahigh sampling rate to match the interpolated sampling rate of the inputsignal. Such an operation can reduce the length of windowing functionwhile maintaining the ACLR performance. Operating the windowing functionat a low sampling rate and upsampling the output signal of the windowingfunction can reduce the length of taps of the windowing function andthus reduces the implementation complexity of the windowing function.FIG. 12 shows an example CFR with upsampling. Graph (a) of FIG. 12 showsCFR waveforms in an example upsampling process. Graph (b) of FIG. 12 isa block diagram illustrating an example CFR with up-sampling.

In some cases, CFR with small window length after up-sampling candeliver similar ACLR as CFR with large window length. FIG. 13 shows anexample upsampling CFR with a first upsampling ratio according to animplementation. Graph (a) of FIG. 13 shows a diagram illustrating a40-tap CFR at 30.72 MHz. As shown, the input signal has a bandwidth of 5MHz, which has a Nyquist frequency of 7.68 MHz. Thus, the input signalhas a sampling rate that is the same as the Nyquist frequency of 7.68MHz. After two stages of 2× upsampling, the signal has a sampling rateof 30.72 MHz. Accordingly, the 40-tap CFR is also operated at the rateof 30.72 MHz. The output of the CFR is then upsampled by 4 times toreach a sampling frequency of 122.88 MHz. Graph (b) of FIG. 13 shows adiagram illustrating a 160-tap CFR at 122.88 MHz. In this case, the CFRis operated at the 122.88 MHz and no upsampling is performed on theoutput signal of CFR. Graph (c) of FIG. 13 shows a spectrum analysis forthe 40-tap CFR at 30.72 MHz and the 160-tap CFR at 122.88 MHz. As shown,the 40-tap CFR at 30.72 MHz and 160-taps CFR at 122.88 MHz deliverapproximately the same ACLR performance. However, increasing thewindowing taps in the CFR by 4 times increases the implementationcomplexity of the CFR filter.

FIG. 14 shows an example upsampling CFR with a second upsampling ratioaccording to an implementation. Graph (a) of FIG. 14 shows a diagramillustrating a 40-tap CFR at 15.36 MHz. As shown, the CFR is operated at2 times the Nyquist frequency of the input signal (7.68 MHz×2=15.36MHz). The output signal of the CFR is up-sampled by 8. Graph (b) of FIG.14 shows a diagram illustrating a 320-tap CFR at 122.88 MHz, withoutfurther upsampling on the output signal of the CFR. Graph (c) of FIG. 14shows a spectrum analysis for the 40-tap CFR at 15.36 MHz and the320-tap CFR at 122.88 MHz. As shown, the 40-tap CFR at 15.36 MHz and320-taps CFR at 122.88 MHz deliver approximately the same ACLRperformance.

In some cases, up-sampling may be used with a digital up converter (DUC)in CFR to reduce silicon resource required to achieve targetingperformance. FIG. 15 shows an example upsampling CFR cascaded withdigital up converter according to an implementation. Graph (a) of FIG.15 shows a block diagram illustrating a 40-tap CFR with up-sampling of8. Graph (b) of FIG. 15 shows a block diagram illustrating a 40-tap CFRwith up-sampling cascaded with DUC. The DUC includes a first stage FIRfilter that interpolates by 2, a second stage FIR filter as a cascadedintegrator-comb (CIC) compensator that compensates the drop response ofCIC, and a CIC filter that interpolates by 4. In this example, the firststage FIR filter may include 27 taps, and the second stage FIR filtermay include 22 taps.

FIG. 16 is a schematic diagram illustrating an example two-carriermulti-rate CFR component 1600 according to an implementation. In somecases, the crest factor reduction component 1600 can be used in atransmitter, e.g., in the user device 102 or in the base station 104 orin the transmitter 200, to reduce the peak amplitude of a source signal.As illustrated, the crest factor reduction component 1600 includescombined signal peak detection component 1606, interpolation components1608 a-b, windowing signal generators 1610 a-b, and interpolationcomponents 1612 a-b. In some cases, the combined signal peak detectioncomponent 1606, interpolation components 1608 a-b, windowing signalgenerators 1610 a-b, and interpolation components 1612 a-b can be usedto generate a peak reduction signal based on an input signal. Themulti-rate CFR component 1600 also includes delay registers 1616 a-b andmultipliers 1618 a-b that are used to mix the input signal with the peakreduction signal to generate an output signal. The multi-rate CFRcomponent 1600 also includes interpolation components 1602 a-b andmultipliers 1604 a-b to perform up-sampling on carrier signals andgenerate the input signals to the combined signal peak detectioncomponent 1606 and the delay registers 1616 a-b.

In some cases, the combined signal peak detection component 1606 and thewindowing signal generators 1610 a-b may process at different samplingrate domains. In one example, the combined signal peak detectioncomponent 1606 may process at high sampling rate domain (e.g., 245.76MHz) to accurately identify the location and magnitude of the peakamplitude of an input signal. The windowing signal generators 1610 a-bmay process at low sampling rate domain (e.g., 15.36 MHz and/or 61.44MHz) to achieve a better ACLR with low power consumption and smallsilicon area. In operation, the interpolation components 1602 a-b mayreceive carrier signals from a first carrier and a second carrier at lowsampling rates. In one example, the bandwidth of CA1 and CA2 can be 5MHz and 20 MHz, respectively. The interpolation components 1602 a-b mayreceive carrier signals at sampling rates that equal to the Nyquistfrequency of 7.68 MHz and 30.72 MHz from the first carrier and thesecond carrier respectively. The interpolation components 1602 a-b mayperform up-sampling on the carrier signals by a factor of N1 and N2,respectively, and work with multipliers 1604 a-b to generate inputsignals to the combined signal peak detection component 1606 at a highsampling rate Fs. In this example, Fs=245.76 MHz, N1=32 and N2=8. Thecombined signal peak detection component 1606 receives the input signalsat the high sampling rate and perform a peak detection on the inputsignals to generate peak detection output signals. The interpolationcomponents 1608 a-b may perform down-sampling on the peak detectionoutput signals to generate windowing input signals to the windowingsignal generators 1610 a-b at low sampling rates. As shown, thedownsampling is performed by a factor of N1/2 and N2/2, respectively. Inthis example, the interpolation components 1608 a-b may generatewindowing input signals at sampling rates of 15.36 MHz and 61.44 MHz forthe first carrier and the second carrier respectively. Then, thewindowing signal generators 1610 a-b can generate windowing outputsignals based on the windowing input signals at low sampling rates. Theinterpolation components 1612 a-b perform up-sampling on the windowingoutput signals and generate peak reduction signals to bring it back tothe high sampling rate Fs (e.g., 245.76 MHz). In some cases, differentdownsampling ratio can be used. For example, instead of using adownsampling ratio of N1/2 and N2/2, the interpolation components 1608a-b can use a downsampling ratio of N1 and N2 to further reduce theoperating rates of the window function 1610 a-b.

In some cases, the up/down sampling ratio (e.g., N1 and N2) of theinterpolation components depend on the signal bandwidth. In some cases,the ratio of the narrow-band signal is higher than that of the widebandsignal. For example, for a first carrier with a bandwidth of 5 MHz, theup/down-sampling ratio of the interpolation components 1602 a, 1608 a,and 1612 a may be 32, 16, and 16 respectively. As a result, for acarrier signal at a sampling rate of 7.68 MHz from the first carrier,the input signal after up-sampling by the interpolation component 1602a, the windowing input signal after down-sampling by the interpolationcomponent 1608 a, and the peak reduction signal after the up-sampling bythe interpolation components 1612 a are generated at the sampling ratesof 245.76 MHz, 15.36 MHz, and 245.76 MHz respectively.

As another example, for a second carrier with a bandwidth of 20 MHz, theup/down-sampling ratio of the interpolation components 1602 b, 1608 b,and 1612 b may be 8, 4, and 4 respectively. As a result, for a carriersignal at a sampling rate of 30.72 MHz from the second carrier, theinput signal after up-sampling by the interpolation component 1602 b,the windowing input signal after down-sampling by the interpolationcomponent 1608 b, and the peak reduction signal after the up-sampling bythe interpolation components 1612 b are generated at the sampling ratesof 245.76 MHz, 61.44 MHz, and 245.76 MHz respectively. As noted, a ratiobetween the windowing input signal sampling rate for the first carrierand the windowing input signal sampling rate or the second carrier isthe same as a ratio between the first bandwidth of the first carrier andthe second bandwidth of the second carrier.

In some cases, the peak reduction signals generated after theup-sampling by the interpolation components 1612 a-b are multiplied by−1 and added to 1 (e.g., using the addition function units 1614 a-b),and then mixed with delayed input signals (e.g., using the multipliers1618 a-b) to generate output signals. In some cases, the peak reductionsignals are applied on both I and Q channels of input signals. Then, theoutput signals for the two carriers are summed by the summation functionunit 1620 to generate a CFR output signal.

FIG. 17 is a schematic diagram illustrating an example two-carriercombined signal peak detection component 1700 (e.g., combined signalpeak detection component 1606 of FIG. 16 ) according to animplementation. In some cases, the combined signal peak detectioncomponent 1700 can be used in a CFR component, e.g., in the carrieraggregation transmitter 200, to detect the peak amplitude of an inputsignal. As illustrated, the combined signal peak detection component1700 includes a summation function unit 1708, a combined envelopcalculator with coordinate rotation digital computer (CORDIC) 1710,clipping signal generators 1712 a-b, window FIR filter with feedback1714 a-b, peak detectors 1716 a-b, and pulse repeaters 1718 a-b. Thesummation function unit 1708, the combined envelop calculator 1710, andthe clipping signal generators 1712 a-b can be used to generate clippingsignals based on input signals and clipping levels for the two carriers.In some cases, the clipping level represents a predetermined peak valuefor the output signal. In some cases, the clipping signal includes thelocation and magnitude of the peaks.

The following equation represents an example clipping function c(n) forgenerating the clipping signals.

${c(n)} = \left\{ {\begin{matrix}{1,} & {\ {{❘{x(n)}❘} \leq \ {{Clipping}\ {Level}}}} \\{\frac{{Clipping}{Level}}{❘{x(n)}❘},} & {\ {{❘{x(n)}❘} > \ {{Clipping}\ {Level}}}}\end{matrix}.} \right.$

In some cases, the clipping signals can have pulse-like waveform whichmay contain very wideband spectrum. In some cases, decimation includedfilter may not be able to down-sample the information (e.g., locationand magnitude of the peaks) without distortion. The window FIR filters(e.g., window FIR filters 1714 a-b), therefore, are used to smooth theclipping signals and keep the information of the peaks. In some cases,the windowing signal generator 700 may be used as the window FIR filters1714 a-b.

In some cases, the peak detectors 1716 a-b receive filter output signalsfrom the window FIR filters 1714 a-b and determine location andmagnitude of the peaks. The output of the peak detection may be repeatedby N/2 by the pulse repeaters 1718 a-b, where N/2 is the predetermineddown-sampling ratio.

FIG. 18 shows the waveforms in an example peak detection process, whichwill be explained in greater detail below with reference to FIG. 19 .FIG. 19 is a flowchart illustrating an example method 1900 for peakdetection. In some cases, the method 1900 may be implemented by a peakdetector (e.g., peak detector 1718 a/b). The method 1900 may begin atblock 1902, where a clipping function is calculated. For example, theclipping function may be calculated using the above-described clippingfunction c(n). In some cases, the clipping function may be calculatedbased on an envelope output signal from the combined envelope calculator1710 and a clipping level.

At block 1904, a complimentary clipping function is generated based onthe calculated clipping function. In some cases, the calculated clippingfunction may be multiplied by −1 and added to 1 to generate thecomplementary clipping function. For example, graph (a) of FIG. 18 showswaveform of the clipping function and waveform of the complimentaryclipping function (e.g., 1−clipping function). In the figure, the peaks'location are indicated by the triangles.

At block 1906, window waveform is generated with feedback FIR. Forexample, the window FIR filters 1714 a-b may be used to smooth theclipping function and generate window waveforms as input signals to thepeak detectors 1716 a-b. Graph (b) of FIG. 18 shows the window waveformgenerated with feedback FIR.

At block 1908, peak detection is performed to obtain location andmagnitude of the peaks. For example, the peak detectors 1716 a-b mayreceive the window waveforms from the window FIR filters 1714 a-b andpinpoint the peaks' location and magnitude. In some cases, the peakdetection may be performed based on slop changes from positive tonegative to determine the peaks' location. Graph (c) of FIG. 18 showsthe locations and magnitudes of the peaks.

At block 1910, the peaks' location and magnitude are duplicated by N.For example, the pulse repeaters 1718 a-b may repeat the output of thepeak detection by N, where N is a predetermined down-sampling ratio.

At block 1912, the output from the duplication of the peak detection isdown-sampled. In some cases, the output may be down-sampled by N,wherein N is a down-sampling ratio that is the same as the number N bywhich the peaks' location and magnitude are duplicated. In some cases, 1out of N samples may be selected from the output signal of the pulserepeaters 1718 a-b. Graph (d) of FIG. 18 shows the down-sampled peakdetection.

FIG. 20 is a schematic diagram illustrating an example windowing signalgenerator 2000 according to an implementation. The windowing signalgenerator 2000 can be used in a multi-rate CFR component, e.g.,multi-rate CFR component 1600. In some cases, the windowing signalgenerator 2000 can be used as the windowing signal generators 1610 a-bin FIG. 16 . In some cases, modification of the real-time mode windowfunction is required for the low sampling rate CFR. For example,compared with the windowing signal generator 700, the complementarycomputation (for example, 1−c(n)) is removed in the windowing signalgenerator 2000 since the down-sampling pulse has accomplished suchcalculation. The windowing signal generator 2000 receives down-samplingpulses to generate window waveform with low sample rate.

FIG. 21 is a schematic diagram illustrating an example multi-carriermulti-rate CFR component 2100 according to an implementation. Asillustrated, the CFR component 2100 receives carrier signals from Mcarriers, as opposed to 2 carriers in FIG. 16 . Note that the CFRcomponent 2100, when M=2, is the same as the CFR component 1600 of FIG.16 . Each of the M carrier signals may be processed by a respective setof interpolation components with different up/down sampling ratios. Insome cases, the windowing signal generators for each of the M carriersignal may have the same number of delay taps (e.g., 40 taps).

FIG. 22 is a schematic diagram illustrating an example multi-carriercombined signal peak detection component 2200. As illustrated, each ofthe M carriers has its own clipping level to achieve the maximal peakreduction results. Note that the peak detection component 2200, whenM=2, is the same as the peak detection component 1700 of FIG. 17 .

FIG. 23 shows a comparison of performance of single-rate and multi-rateCFR. As shown in graph (a) of FIG. 23 , the carrier CA2 has a power thatis lower than that of the carrier CA1 by 30 dB. The poor ACLRimprovement of CA1 from single rate CFR (120 taps) degrades EVM of theadjacent carrier, CA2. The PAPR may not be further reduced since the EVMof CA2 has been reduced to −29 dB already. Graph (b) of FIG. 23 showsthat, with the multi-rate CFR (20 taps), the ACLR is improved by 0.6 dB(6.4 dB-5.8 dB) more peak reduction. Graphs (c) and (d) of FIG. 23 showthat, with the multi-rate CFR (20 taps), the ACLR is improved with 7 dBcmore as opposed to with the single-rate CFR, and that the EVM of bothcarriers is lower than −30 dB with multi-rate CFR.

FIG. 24 shows a comparison of performance of single-rate and multi-rateCFR. As shown in graph (a) of FIG. 24 , the carrier CA2 has a powerclose to that of the carrier CA1. Single rate CFR delivers unbalancedACLR/EVM performance and may not use silicon resource efficiently. Forexample, the ACLR of carrier CA2 is excessively good with 120 taps. Butthe ACLR of carrier CA1 is poor and can interfere with carrier CA2.Multi-rate CFR delivers balanced ACLR/EVM performance with lower PAPRand silicon resource. As shown in graph (b) of FIG. 24 , multi-rate CFRreduces 0.2 dB more than single-rate CFR. Graphs (c) and (d) of FIG. 24show that multi-rate CFR has better balanced ACLR/EVM performance.Multi-rate CFR, therefore, demonstrates better performance than thesingle rate CFR with equal power of the two carrier aggregationconfiguration.

FIG. 25 is a flow chart illustrating an example method 2500 for reducingcrest factors. In some cases, the method 2500 can be implemented by amulti-rate CFR component (e.g., multi-rate CFR component 1600 or 2100).

The method 2500 may begin at block 2502 where a plurality of firstsamples of a first input signal are received. In some cases, theplurality of first samples are generated at a first sampling rate (e.g.,245.76 MHz). In some cases, the first input signal includes an inputsignal of a first carrier. In some cases, a plurality of second samplesof a second input signal are also received. The plurality of secondsamples can be generated at the first sampling rate, and the secondinput signal can include an input signal of a second carrier. In somecases, the first carrier has a first bandwidth (e.g., 5 MHz) and thesecond carrier has a second bandwidth (e.g. 20 MHz).

At block 2504, a first peak detection is performed on the plurality offirst samples to generate a plurality of first peak detection outputsamples. In some cases, a second peak detection is performed on theplurality of second samples to generate a plurality of second peakdetection output samples.

At block 2506, a plurality of first windowing input samples aregenerated at a second sampling rate (e.g., 15.36 MHz) by down-samplingthe plurality of first peak detection output samples. In some cases, aplurality of second windowing input samples are generated at a thirdsampling rate (e.g., 61.44 MHz) by down-sampling the plurality of secondpeak detection output samples. In some cases, a ratio between the secondsampling rate and the third sampling rate is the same as a ratio betweenthe first bandwidth of the first carrier and the second bandwidth of thesecond carrier.

At block 2508, a plurality of first windowing output samples aregenerated based on the plurality of first windowing input samples. Insome cases, a plurality of second windowing output samples are generatedbased on the plurality of second windowing input samples.

At block 2510, a plurality of first peak reduction samples are generatedat the first sampling rate by upsampling the plurality of firstwindowing output samples. In some cases, a plurality of second peakreduction samples are generated at the second sampling rate byupsampling the plurality of second windowing output samples.

At block 2512, a first output signal is generated based on the pluralityof first samples and the plurality of first peak reduction samples. Insome cases, generating the first output signal includes applying theplurality of first peak reduction samples on both I and Q channels of onthe plurality of first samples. In some cases, a second output signal isgenerated based on the plurality of second samples and the plurality ofsecond peak reduction samples.

In some cases, the actions as described above in method 2500 on thefirst and second carriers are done in parallel/simultaneously.

FIG. 26 is a schematic diagram illustrating an example structure of anelectronic device 2600 described in the present disclosure, according toan implementation. The electronic device 2600 includes one or moreprocessors 2602, a memory 2604, a peak detection circuit 2606, adownsampling circuit 2608, a windowing signal generating circuit 2610,and an upsampling circuit 2612. In some implementations, electronicdevice 2600 can further include one or more circuits for performing anyone or a combination of steps described in the present disclosure.

Described implementations of the subject matter can include one or morefeatures, alone or in combination.

In a first implementation, a method for reducing crest factors includes:receiving a plurality of first samples of a first input signal, whereinthe plurality of first samples are generated at a first sampling rate;performing a first peak detection based on the plurality of firstsamples to generate a plurality of first peak detection output samples;downsampling the plurality of first peak detection output samples togenerate a plurality of first windowing input samples at a secondsampling rate; generating a plurality of first windowing output samplesbased on the plurality of first windowing input samples; upsampling theplurality of first windowing output samples to generate a plurality offirst peak reduction samples at the first sampling rate; and generatinga first output signal based on the plurality of first samples and theplurality of first peak reduction samples.

The foregoing and other described implementations can each, optionally,include one or more of the following features:

A first feature, combinable with any of the following features, wherethe first input signal includes an input signal of a first carrier, andthe method further includes: receiving a plurality of second samples ofa second input signal, wherein the plurality of second samples aregenerated at the first sampling rate, and the second input signalcomprises an input signal of a second carrier; performing a second peakdetection based on the plurality of second samples to generate aplurality of second peak detection output samples; downsampling theplurality of second peak detection output samples to generate aplurality of second windowing input samples at a third sampling rate;generating a plurality of second windowing output samples based on theplurality of second windowing input samples; upsampling the plurality ofsecond windowing output samples to generate a plurality of second peakreduction samples at the second sampling rate; and generating a secondoutput signal based on the plurality of second samples and the pluralityof second peak reduction samples.

A second feature, combinable with any of the previous or followingfeatures, where a ratio between the second sampling rate and the thirdsampling rate is the same as a ratio between a first bandwidth of thefirst carrier and a second bandwidth of the second carrier.

A third feature, combinable with any of the previous or followingfeatures, where the generating the first output signal comprisesapplying the plurality of first peak reduction samples on both I and Qchannels of the plurality of first samples.

A fourth feature, combinable with any of the previous or followingfeatures, where performing the first peak detection includes: generatinga plurality of first clipping samples based on the plurality of firstsamples and a first clipping level; generating a plurality of firstwindow filtering output samples based on the plurality of first clippingsamples; and generating the plurality of first peak detection outputsamples based on the plurality of first window filtering output samples.

A fifth feature, combinable with any of the previous or followingfeatures, where performing the second peak detection includes:generating a plurality of second clipping samples based on the pluralityof second samples and a second clipping level; generating a plurality ofsecond window filtering output samples based on the plurality of secondclipping samples; and generating the plurality of second peak detectionoutput samples based on the plurality of second window filtering outputsamples.

A sixth feature, combinable with any of the previous or followingfeatures, where the plurality of first samples are generated byupsampling a first carrier signal of the first carrier, and theplurality of second samples are generated by upsampling a second carriersignal of the second carrier.

A seventh feature, combinable with any of the previous features, wherethe plurality of first windowing output samples and the plurality ofsecond windowing output samples are generated using a same number ofdelay taps.

In a second implementation, an electronic device includes: anon-transitory memory storage comprising instructions; and one or morehardware processors in communication with the memory storage, whereinthe one or more hardware processors execute the instructions to: receivea plurality of first samples of a first input signal, wherein theplurality of first samples are generated at a first sampling rate;perform a first peak detection based on the plurality of first samplesto generate a plurality of first peak detection output samples;downsample the plurality of first peak detection output samples togenerate a plurality of first windowing input samples at a secondsampling rate; generate a plurality of first windowing output samplesbased on the plurality of first windowing input samples; upsample theplurality of first windowing output samples to generate a plurality offirst peak reduction samples at the first sampling rate; and generate afirst output signal based on the plurality of first samples and theplurality of first peak reduction samples.

The foregoing and other described implementations can each, optionally,include one or more of the following features:

A first feature, combinable with any of the following features, wherethe first input signal includes an input signal of a first carrier, andthe one or more hardware processors further execute the instructions to:receive a plurality of second samples of a second input signal, whereinthe plurality of second samples are generated at the first samplingrate, and the second input signal comprises an input signal of a secondcarrier; perform a second peak detection based on the plurality ofsecond samples to generate a plurality of second peak detection outputsamples; downsample the plurality of second peak detection outputsamples to generate a plurality of second windowing input samples at athird sampling rate; generate a plurality of second windowing outputsamples based on the plurality of second windowing input samples;upsample the plurality of second windowing output samples to generate aplurality of second peak reduction samples at the second sampling rate;and generate a second output signal based on the plurality of secondsamples and the plurality of second peak reduction samples.

A second feature, combinable with any of the previous or followingfeatures, where a ratio between the second sampling rate and the thirdsampling rate is the same as a ratio between a first bandwidth of thefirst carrier and a second bandwidth of the second carrier.

A third feature, combinable with any of the previous or followingfeatures, where the generating the first output signal includes applyingthe plurality of first peak reduction samples on both I and Q channelsof the plurality of first samples.

A fourth feature, combinable with any of the previous or followingfeatures, where performing the first peak detection includes: generatinga plurality of first clipping samples based on the plurality of firstsamples and a first clipping level; generating a plurality of firstwindow filtering output samples based on the plurality of first clippingsamples; and generating the plurality of first peak detection outputsamples based on the plurality of first window filtering output samples.

A fifth feature, combinable with any of the previous or followingfeatures, where performing the second peak detection includes:generating a plurality of second clipping samples based on the pluralityof second samples and a second clipping level; generating a plurality ofsecond window filtering output samples based on the plurality of secondclipping samples; and generating the plurality of second peak detectionoutput samples based on the plurality of second window filtering outputsamples.

A sixth feature, combinable with any of the previous or followingfeatures, where the plurality of first samples are generated byupsampling a first carrier signal of the first carrier, and theplurality of second samples are generated by upsampling a second carriersignal of the second carrier.

A seventh feature, combinable with any of the previous features, wherethe plurality of first windowing output samples and the plurality ofsecond windowing output samples are generated using a same number ofdelay taps.

In a third implementation, a non-transitory computer-readable mediumstoring computer instructions for reducing crest factors, that whenexecuted by one or more hardware processors, cause the one or morehardware processors to perform operations including: receiving aplurality of first samples of a first input signal, wherein theplurality of first samples are generated at a first sampling rate;performing a first peak detection based on the plurality of firstsamples to generate a plurality of first peak detection output samples;downsampling the plurality of first peak detection output samples togenerate a plurality of first windowing input samples at a secondsampling rate; generating a plurality of first windowing output samplesbased on the plurality of first windowing input samples; upsampling theplurality of first windowing output samples to generate a plurality offirst peak reduction samples at the first sampling rate; and generatinga first output signal based on the plurality of first samples and theplurality of first peak reduction samples.

The foregoing and other described implementations can each, optionally,include one or more of the following features:

A first feature, combinable with any of the following features, wherethe first input signal includes an input signal of a first carrier, andthe operations further include: receiving a plurality of second samplesof a second input signal, wherein the plurality of second samples aregenerated at the first sampling rate, and the second input signalcomprises an input signal of a second carrier; performing a second peakdetection based on the plurality of second samples to generate aplurality of second peak detection output samples; downsampling theplurality of second peak detection output samples to generate aplurality of second windowing input samples at a third sampling rate;generating a plurality of second windowing output samples based on theplurality of second windowing input samples; upsampling the plurality ofsecond windowing output samples to generate a plurality of second peakreduction samples at the second sampling rate; and generating a secondoutput signal based on the plurality of second samples and the pluralityof second peak reduction samples.

A second feature, combinable with any of the previous or followingfeatures, where a ratio between the second sampling rate and the thirdsampling rate is the same as a ratio between a first bandwidth of thefirst carrier and a second bandwidth of the second carrier.

A third feature, combinable with any of the previous or followingfeatures, where the generating a first output signal comprises applyingthe plurality of first peak reduction samples on both I and Q channelsof the plurality of first samples.

Implementations of the subject matter and the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, in tangibly embodied computer software or firmware, incomputer hardware, including the structures disclosed in thisspecification and their structural equivalents, or in combinations ofone or more of them. Implementations of the subject matter described inthis specification can be implemented as one or more computer programs,that is, one or more modules of computer program instructions encoded ona tangible, non-transitory, computer-readable computer-storage mediumfor execution by, or to control the operation of, data processingapparatus. Alternatively, or additionally, the program instructions canbe encoded in/on an artificially generated propagated signal, forexample, a machine-generated electrical, optical, or electromagneticsignal that is generated to encode information for transmission tosuitable receiver apparatus for execution by a data processingapparatus. The computer-storage medium can be a machine-readable storagedevice, a machine-readable storage substrate, a random or serial accessmemory device, or a combination of computer-storage mediums.

The terms “data processing apparatus,” and “computer,” (or equivalent asunderstood by one of ordinary skill in the art) refer to data processinghardware and encompass all kinds of apparatus, devices, and machines forprocessing data, including by way of example, a programmable processor,a computer, or multiple processors or computers. The apparatus can alsobe or further include special purpose logic circuitry, for example, aCentral Processing Unit (CPU), a Field Programmable Gate Array (FPGA),or an Application-specific Integrated Circuit (ASIC). In someimplementations, the data processing apparatus or special purpose logiccircuitry (or a combination of the data processing apparatus or specialpurpose logic circuitry) may be hardware- or software-based (or acombination of both hardware- and software-based). The apparatus canoptionally include code that creates an execution environment forcomputer programs, for example, code that constitutes processorfirmware, a protocol stack, a database management system, an operatingsystem, or a combination of execution environments. The presentdisclosure contemplates the use of data processing apparatuses with orwithout conventional operating systems, for example LINUX, UNIX,WINDOWS, MAC OS, ANDROID, IOS, or any other suitable conventionaloperating system.

A computer program, which may also be referred to or described as aprogram, software, a software application, a module, a software module,a script, or code can be written in any form of programming language,including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program may, butneed not, correspond to a file in a file system. A program can be storedin a portion of a file that holds other programs or data, for example,one or more scripts stored in a markup language document, in a singlefile dedicated to the program in question, or in multiple coordinatedfiles, for example, files that store one or more modules, sub-programs,or portions of code. A computer program can be deployed to be executedon one computer or on multiple computers that are located at one site ordistributed across multiple sites and interconnected by a communicationnetwork. While portions of the programs illustrated in the variousfigures are shown as individual modules that implement the variousfeatures and functionality through various objects, methods, or otherprocesses, the programs may instead include a number of sub-modules,third-party services, components, libraries, and such, as appropriate.Conversely, the features and functionality of various components can becombined into single components, as appropriate. Thresholds used to makecomputational determinations can be statically, dynamically, or bothstatically and dynamically determined.

The methods, processes, or logic flows described in this specificationcan be performed by one or more programmable computers executing one ormore computer programs to perform functions by operating on input dataand generating output. The methods, processes, or logic flows can alsobe performed by, and apparatus can also be implemented as, specialpurpose logic circuitry, for example, a CPU, an FPGA, or an ASIC.

Computers suitable for the execution of a computer program can be basedon general or special purpose microprocessors, both, or any other kindof CPU. Generally, a CPU will receive instructions and data from a ROMor a Random Access Memory (RAM), or both. The essential elements of acomputer are a CPU, for performing or executing instructions, and one ormore memory devices for storing instructions and data. Generally, acomputer will also include, or be operatively coupled to, receive datafrom or transfer data to, or both, one or more mass storage devices forstoring data, for example, magnetic, magneto-optical disks, or opticaldisks. However, a computer need not have such devices. Moreover, acomputer can be embedded in another device, for example, a mobiletelephone, a Personal Digital Assistant (PDA), a mobile audio or videoplayer, a game console, a Global Positioning System (GPS) receiver, or aportable storage device, for example, a Universal Serial Bus (USB) flashdrive, to name just a few.

Computer-readable media (transitory or non-transitory, as appropriate)suitable for storing computer program instructions and data includesnon-volatile memory, media and memory devices, including by way ofexample, semiconductor memory devices, for example, ErasableProgrammable Read-Only Memory (EPROM), Electrically ErasableProgrammable Read-Only Memory (EEPROM), and flash memory devices;magnetic disks, for example, internal hard disks or removable disks;magneto-optical disks; and CD-ROM, DVD+/−R, DVD-RAM, and DVD-ROM disks.The memory may store various objects or data, including caches, classes,frameworks, applications, backup data, jobs, web pages, web pagetemplates, database tables, repositories storing dynamic information,and any other appropriate information including any parameters,variables, algorithms, instructions, rules, constraints, or referencesthereto. Additionally, the memory may include any other appropriatedata, such as logs, policies, security or access data, reporting files,as well as others. The processor and the memory can be supplemented by,or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, implementations of the subjectmatter described in this specification can be implemented on a computerhaving a display device, for example, a Cathode Ray Tube (CRT), LiquidCrystal Display (LCD), Light Emitting Diode (LED), or plasma monitor,for displaying information to the user and a keyboard and a pointingdevice, for example, a mouse, trackball, or trackpad by which the usercan provide input to the computer. Input may also be provided to thecomputer using a touchscreen, such as a tablet computer surface withpressure sensitivity, a multi-touch screen using capacitive or electricsensing, or other type of touchscreen. Other kinds of devices can beused to provide for interaction with a user as well; for example,feedback provided to the user can be any form of sensory feedback, forexample, visual feedback, auditory feedback, or tactile feedback; andinput from the user can be received in any form, including acoustic,speech, or tactile input. In addition, a computer can interact with auser by sending documents to and receiving documents from a device thatis used by the user; for example, by sending web pages to a web browseron a user's client device in response to requests received from the webbrowser.

Implementations of the subject matter described in this specificationcan be implemented in a computing system that includes a back-endcomponent, for example, as a data server, or that includes a middlewarecomponent, for example, an application server, or that includes afront-end component, for example, a client computer having a graphicaluser interface or a Web browser through which a user can interact withan implementation of the subject matter described in this specification,or any combination of one or more such back-end, middleware, orfront-end components. The components of the system can be interconnectedby any form or medium of wireline or wireless digital data communication(or a combination of data communication), for example, a communicationnetwork. Examples of communication networks include a Local Area Network(LAN), a Radio Access Network (RAN), a Metropolitan Area Network (MAN),a Wide Area Network (WAN), Worldwide Interoperability for MicrowaveAccess (WIMAX), a Wireless Local Area Network (WLAN) using, for example,802.11 a/b/g/n or 802.20 (or a combination of 802.11x and 802.20 orother protocols consistent with this disclosure), all or a portion ofthe Internet, or any other communication system or systems at one ormore locations (or a combination of communication networks). The networkmay communicate with, for example, Internet Protocol (IP) packets, FrameRelay frames, Asynchronous Transfer Mode (ATM) cells, voice, video,data, or other suitable information (or a combination of communicationtypes) between network addresses.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinvention or on the scope of what may be claimed, but rather asdescriptions of features that may be specific to particularimplementations of particular inventions. Certain features that aredescribed in this specification in the context of separateimplementations can also be implemented, in combination, in a singleimplementation. Conversely, various features that are described in thecontext of a single implementation can also be implemented in multipleimplementations, separately, or in any suitable sub-combination.Moreover, although previously described features may be described asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can, in some cases, beexcised from the combination, and the claimed combination may bedirected to a sub-combination or variation of a sub-combination.

Particular implementations of the subject matter have been described.Other implementations, alterations, and permutations of the describedimplementations are within the scope of the following claims as will beapparent to those skilled in the art. While operations are depicted inthe drawings or claims in a particular order, this should not beunderstood as requiring that such operations be performed in theparticular order shown or in sequential order, or that all illustratedoperations be performed (some operations may be considered optional), toachieve desirable results. In certain circumstances, multitasking orparallel processing (or a combination of multitasking and parallelprocessing) may be advantageous and performed as deemed appropriate.

Moreover, the separation or integration of various system modules andcomponents in the previously described implementations should not beunderstood as requiring such separation or integration in allimplementations, and it should be understood that the described programcomponents and systems can generally be integrated together in a singlesoftware product or packaged into multiple software products.

Accordingly, the previously described example implementations do notdefine or constrain this disclosure. Other changes, substitutions, andalterations are also possible without departing from the spirit andscope of this disclosure.

Furthermore, any claimed implementation is considered to be applicableto at least a computer-implemented method; a non-transitory,computer-readable medium storing computer-readable instructions toperform the computer-implemented method; and a computer systemcomprising a computer memory interoperably coupled with a hardwareprocessor configured to perform the computer-implemented method or theinstructions stored on the non-transitory, computer-readable medium.

1-20. (canceled)
 21. A method for reducing crest factors, the methodcomprising: receiving a plurality of first samples of a first inputsignal, the plurality of first samples generated at a first samplingrate; performing a first peak detection based on the plurality of firstsamples to generate a plurality of first peak detection output samples;downsampling the plurality of first peak detection output samples togenerate a plurality of first windowing input samples at a secondsampling rate; generating a plurality of first windowing output samplesbased on the plurality of first windowing input samples; upsampling theplurality of first windowing output samples to generate a plurality offirst peak reduction samples at the first sampling rate; and generatinga first output signal based on the plurality of first samples and theplurality of first peak reduction samples.
 22. The method according toclaim 21, wherein the first input signal comprises an input signal of afirst carrier, and the method further comprises: receiving a pluralityof second samples of a second input signal, wherein the plurality ofsecond samples are generated at the first sampling rate, and the secondinput signal comprises an input signal of a second carrier; performing asecond peak detection based on the plurality of second samples togenerate a plurality of second peak detection output samples;downsampling the plurality of second peak detection output samples togenerate a plurality of second windowing input samples at a thirdsampling rate; generating a plurality of second windowing output samplesbased on the plurality of second windowing input samples; upsampling theplurality of second windowing output samples to generate a plurality ofsecond peak reduction samples at the second sampling rate; andgenerating a second output signal based on the plurality of secondsamples and the plurality of second peak reduction samples.
 23. Themethod according to claim 22, wherein a ratio between the secondsampling rate and the third sampling rate is the same as a ratio betweena first bandwidth of the first carrier and a second bandwidth of thesecond carrier.
 24. The method according to claim 22, wherein thegenerating the first output signal comprises applying the plurality offirst peak reduction samples on both I and Q channels of the pluralityof first samples.
 25. The method according to claim 22, whereinperforming the first peak detection comprises: generating a plurality offirst clipping samples based on the plurality of first samples and afirst clipping level; generating a plurality of first window filteringoutput samples based on the plurality of first clipping samples; andgenerating the plurality of first peak detection output samples based onthe plurality of first window filtering output samples.
 26. The methodaccording to claim 25, wherein performing the second peak detectioncomprises: generating a plurality of second clipping samples based onthe plurality of second samples and a second clipping level; generatinga plurality of second window filtering output samples based on theplurality of second clipping samples; and generating the plurality ofsecond peak detection output samples based on the plurality of secondwindow filtering output samples.
 27. The method according to claim 22,wherein the plurality of first samples are generated by upsampling afirst carrier signal of the first carrier, and the plurality of secondsamples are generated by upsampling a second carrier signal of thesecond carrier.
 28. The method according to claim 22, wherein theplurality of first windowing output samples and the plurality of secondwindowing output samples are generated using a same number of delaytaps.
 29. An electronic device comprising: a non-transitory memorystorage comprising instructions; and one or more hardware processors incommunication with the non-transitory memory storage, the one or morehardware processors configured to execute the instructions to cause theelectronic device to: receive a plurality of first samples of a firstinput signal, the plurality of first samples generated at a firstsampling rate; perform a first peak detection based on the plurality offirst samples to generate a plurality of first peak detection outputsamples; downsample the plurality of first peak detection output samplesto generate a plurality of first windowing input samples at a secondsampling rate; generate a plurality of first windowing output samplesbased on the plurality of first windowing input samples; upsample theplurality of first windowing output samples to generate a plurality offirst peak reduction samples at the first sampling rate; and generate afirst output signal based on the plurality of first samples and theplurality of first peak reduction samples.
 30. The electronic deviceaccording to claim 29, wherein the first input signal comprises an inputsignal of a first carrier, and the one or more hardware processorsfurther execute the instructions to: receive a plurality of secondsamples of a second input signal, wherein the plurality of secondsamples are generated at the first sampling rate, and the second inputsignal comprises an input signal of a second carrier; perform a secondpeak detection based on the plurality of second samples to generate aplurality of second peak detection output samples; downsample theplurality of second peak detection output samples to generate aplurality of second windowing input samples at a third sampling rate;generate a plurality of second windowing output samples based on theplurality of second windowing input samples; upsample the plurality ofsecond windowing output samples to generate a plurality of second peakreduction samples at the second sampling rate; and generate a secondoutput signal based on the plurality of second samples and the pluralityof second peak reduction samples.
 31. The electronic device according toclaim 30, wherein a ratio between the second sampling rate and the thirdsampling rate is the same as a ratio between a first bandwidth of thefirst carrier and a second bandwidth of the second carrier.
 32. Theelectronic device according to claim 30, wherein generating the firstoutput signal comprises applying the plurality of first peak reductionsamples on both I and Q channels of the plurality of first samples. 33.The electronic device according to claim 30, wherein performing thefirst peak detection comprises: generating a plurality of first clippingsamples based on the plurality of first samples and a first clippinglevel; generating a plurality of first window filtering output samplesbased on the plurality of first clipping samples; and generating theplurality of first peak detection output samples based on the pluralityof first window filtering output samples.
 34. The electronic deviceaccording to claim 30, wherein performing the second peak detectioncomprises: generating a plurality of second clipping samples based onthe plurality of second samples and a second clipping level; generatinga plurality of second window filtering output samples based on theplurality of second clipping samples; and generating the plurality ofsecond peak detection output samples based on the plurality of secondwindow filtering output samples.
 35. The electronic device according toclaim 30, wherein the plurality of first samples are generated byupsampling a first carrier signal of the first carrier, and theplurality of second samples are generated by upsampling a second carriersignal of the second carrier.
 36. The electronic device according toclaim 30, wherein the plurality of first windowing output samples andthe plurality of second windowing output samples are generated using asame number of delay taps.
 37. A non-transitory computer-readable mediumstoring computer instructions for reducing crest factor, that whenexecuted by one or more hardware processors of an electronic device,cause the electronic device to perform operations comprising: receivinga plurality of first samples of a first input signal, the plurality offirst samples generated at a first sampling rate; performing a firstpeak detection based on the plurality of first samples to generate aplurality of first peak detection output samples; downsampling theplurality of first peak detection output samples to generate a pluralityof first windowing input samples at a second sampling rate; generating aplurality of first windowing output samples based on the plurality offirst windowing input samples; upsampling the plurality of firstwindowing output samples to generate a plurality of first peak reductionsamples at the first sampling rate; and generating a first output signalbased on the plurality of first samples and the plurality of first peakreduction samples.
 38. The non-transitory computer-readable mediumaccording to claim 37, wherein the first input signal comprises an inputsignal of a first carrier, and the operations further comprise:receiving a plurality of second samples of a second input signal,wherein the plurality of second samples are generated at the firstsampling rate, and the second input signal comprises an input signal ofa second carrier; performing a second peak detection based on theplurality of second samples to generate a plurality of second peakdetection output samples; downsampling the plurality of second peakdetection output samples to generate a plurality of second windowinginput samples at a third sampling rate; generating a plurality of secondwindowing output samples based on the plurality of second windowinginput samples; upsampling the plurality of second windowing outputsamples to generate a plurality of second peak reduction samples at thesecond sampling rate; and generating a second output signal based on theplurality of second samples and the plurality of second peak reductionsamples.